This invention relates to a distance measuring method and means.
Requirements exist in certain spheres of activity for means whereby distances from a given point to one or more other point may be ascertained rapidly and at least reasonably accurately, without the necessity of using a measuring tape or similar means requiring physical connection between those point.
Various means already exist for achieving these requirements. For instance, the well-known optical range finder operates on the principle of aligning two mirror images of the object to which the distance is to be measured, the distance then being read off a scale on the instrument, determined by the relative positions of the mirrors.
Another means for achieving these requirements is the Electronic Distance Meter, or EDM, which operates on the principle of transmitting a modulated beam (usually infra-red) which is reflected back to the instrument from a reflector positioned at the point to which the distance is to be measured. A computer system built into the instrument calculates the distance by comparing the return signal with that originally transmitted. The distance so calculated is displayed as a readout on the display unit of the instrument.
Yet another means for achieving these requirements is by means of an impulse type EDM. This type operates on the principle of transmitting a very brief impulse, and the distance is determined by measuring the time elapsed from when the impulse signal is transmitted until the return signal is received.
The distance is then displayed on the display unit of the instrument. Certain variations of the impulse type EDM, have the advantage of being able to detect the return signal from the object to which the distance is to be measured without the use of a reflector.
All of the foregoing types of distance measuring instruments do, however, have disadvantages for use in certain applications, for example under the dark and restricted conditions pertaining in underground mines. For instance, the optical range finder is often impossible to use in dark conditions. The modulated beam type EDM requires a reflector positioned at the point to be measured, and both the modulated beam and the impulse type EDM have to be very precisely aligned onto the point where distance is to be measured, an extremely difficult and time consuming operation in, for example, underground mining conditions.